The present invention relates to a method of manufacturing a composite-material product, such as a container, a tubular product, a wing or another structure, reinforced by, for example, reinforcing fibers. More particularly, the present invention relates to a method of manufacturing a structure made of fiber-reinforced plastic or the like by using a mold, for example, a core, the removal of which from the structure has been difficult and which is made of a biodegradable material.
When a composite-material product reinforced by carbon-fiber-reinforced plastic (hereinafter called xe2x80x9cCFRPxe2x80x9d) or glass-fiber-reinforced plastic (hereinafter called xe2x80x9cGFRPxe2x80x9d), for example, a hollow structure having an undercut, is manufactured, a method structured as shown in FIG. 30 has been employed.
That is, a metal and split mandrel 401 composed of a shell 401a and a core 401b having shapes corresponding to a shape attempted to be molded is prepared. Then, CFRP or GFRP is laminated on the outer surface of the shell 401a of the split mandrel 401 so that a reinforcing-fiber-reinforced resin layer 402 is formed. The reinforcing-fiber-reinforced resin layer 402 is hardened with heat or at room temperatures. Then, the shell 401a and core 401b of the split mandrel 401 are mechanically decomposed (separated) so as to be removed from the inside portion of the reinforcing-fiber-reinforced resin layer 402. As a result, a hollow structure 403 is molded.
If the shape of the hollow structure attempted to be molded by the metal and split mandrel is too complicated to easily be removed by mechanical decomposition after the molding process has been completed, the following method is employed. That is, the mandrel is made of a metal material having a low melting point. Moreover, the CFRP or GFRP is laminated on the outer surface of the mandrel as described above to form the fiber-reinforced resin layer. Then, the fiber-reinforced resin layer is hardened at room temperatures, and then the mandrel is heated at appropriate temperatures so as to be melted and removed.
Another method is known with which the mandrel is made of a material which can be melted with a chemical. Another method is known with which the mandrel is made of collapsible plaster which is crushed so as to be removed after the molding process has been completed. The above-mentioned manufacturing methods have been employed to mold a product, such as a duct 404 including a warped portion 404a and a branch portion 404b, as shown in FIG. 31(a). Also the foregoing methods have been employed to mold, for example, a tubular member 405 having bent portions 405a at two ends thereof, as shown in FIG. 31(b).
However, the split mandrel cannot easily be manufactured and thus the manufacturing cost is enlarged. If a complicated shape is attempted to be formed, the separation and removal which are performed after the molding process has been completed cannot easily be performed as well as the difficulty in manufacturing the same. In this case, excessively large force is added to the molded product and, therefore, the molded product is deformed or broken.
Any one of the above-mentioned method of removing the mandrel by heating and melting the same, the method of removing the mandrel by melting the same by using a chemical and the method of removing the mandrel by crushing the collapsible plaster require a large number of steps. Thus, all of the foregoing methods suffer from unsatisfactory productivity. When a molded product having a complicated shape is attempted to be manufactured, the mandrel cannot completely be removed. When the core is manufactured by aluminum, the solvent of the chemical is sodium hydroxide. However, a great cost is required to perform disposal of sodium hydroxide after the core has been dissolved. What is worse, environmental pollution is undesirably caused to take place.
In recent years, weight reduction and increase in the strength have been required. Therefore, prepreg has energetically been developed which contains thermosetting resin, such as epoxy resin or unsaturated polyester, serving as a matrix thereof and a reinforcing material, such as carbon fibers, aramide fibers or glass fibers, added thereto. Therefore, the needs for a variety of products containing the prepreg have considerably been grown. In addition, the needs for a composite-material product such that thermoplastic resin, such as nylon or polyether-ether ketone (PEEK), is used as the matrix have been grown.
Since the prepreg of the foregoing type is a material having excellent characteristics which enable light weight and strong structure to be manufactured, it can be considered that a composite material is an advantageous material to make various elements for use in an extreme condition in, for example, an aerospace industrial field. Since the foregoing structures usually have complicated shapes, complicated processes are required to manufacture the foregoing structures.
When the thermosetting resin or the thermoplastic resin is employed as the matrix of the core of the honeycomb for use in the composite-material structure and long carbon-fiber-reinforced plastic (hereinafter called xe2x80x9cCFRPxe2x80x9d) or the glass-fiber-reinforced plastic (hereinafter called xe2x80x9cGFRPxe2x80x9d) is employed as the reinforcing fiber, the prepreg must be laminated in a trapezoidal mold having asperities so as to be hardened by an autoclave or a pressing machine.
A fact is known that a structure that the long fiber CFRP or GFRP employed as the reinforcing fiber of the core material enables a strong and rigid honeycomb plate to be manufactured. However, there arises a problem in that long time and great effort are required to inject the material and to perform a laminating process when a waveform plate is molded to manufacture the core member. Further, since the honeycomb structure such as the honeycomb plate has normally a directional property, etc., it has been difficult to design and manufacture the three-dimensional honeycomb structure. However, the honeycomb plate suffers from unsatisfactory strength against a load added in a direction perpendicular to the longitudinal plate.
When an airplane or a wing structure such as wings or fan""s blades are manufactured by using the known honeycomb structures, the main body of the wing 411 is constituted by honeycomb cores 412 having lower densities, that is, a large cell size (the length of one side of a hexagon is long), as shown in FIG. 32. In this case, the weight of the wing 411 can be reduced. If the outer surface of the wing 411 is attempted to be smoothed or if the resistance against collision with an object is attempted to be somewhat enlarged, it is preferable that honeycomb cores 413 each having a high density, that is, a small cell size (the length of one side of a hexagon is short) is employed.
Therefore, a two-layer structure has been employed which is composed of the honeycomb cores 412 having the large cell size and the honeycomb cores 413 having the small cell size which are laminated through the prepreg 414. However, the manufacturing process requires long time and great effort and a complicated three-dimensional curved surface cannot easily be manufactured. Therefore, the above-mentioned structure cannot practically be employed. Although the honeycomb can be preformed at high temperatures, a large heat-resisting mold is required to preform the honeycomb. Thus, the manufacturing cost is enlarged.
When a three-dimensional curved surface is manufactured by using the honeycomb, a core material 415 must be cut to form a rectangular block into the three-dimensional curved surface, as shown in FIG. 33(a). As an alternative to this, a honeycomb core material 416 for forming a three-dimensional curved surface must be employed, as shown in FIG. 33(b). In either case, the manufacturing cost cannot be reduced. Therefore, another requirement is imposed to manufacture a complicated structure of the foregoing type by using the composite material at a low cost.
To achieve the above-mentioned objects, a first characteristic of the present invention lies in that a core or another mold for molding a required structure is made of a biodegradable material, followed by manufacturing the structure by using the mold and followed by biochemically decomposing the mold.
The biodegradable material for use to make the above-mentioned mold is a polymer which can be degraded with microorganisms, enzymes or another biochemical means or a mixed material of the polymer and a biodegradable material. Each of the above-mentioned material is biochemically degraded into e.g., water and carbon dioxide after the structure has been molded. Therefore, the material can easily and completely be removed from the structure. Since the biodegradable material can be degraded into the harmless substances, the disposal cost can be reduced and a problem of environmental pollution does not arise.
The present invention has another characteristic for efficiently degrading the mold, such as the core, made of the biodegradable material. For example, a structure manufactured by using the above-mentioned mold is accommodated in a degrading tank. In the foregoing tank, a solution containing biochemically active substances, such as microorganisms, enzymes or the like, is circulated. The solution is added with substances for enhancing the action of the biochemically active substances, for example, nutrients for the microorganisms. The temperature, pH, components and so forth of the solution which is circulated in the degrading tank are adjusted. Moreover, substances, for example, metabolites of the microorganisms, for example, carbon dioxide, which deteriorate the action of the biochemically active substances are removed from the degrading tank.
The mold made of the above-mentioned biodegradable material has a structure which enhances the biochemical degradation. If the mold is employed as the core, the core is formed into a hollow shape to maintain a passage and surface of contact with the solution containing the biochemically active substances. The mold is made of open-cell foam composed of the biodegradable material to enhance passage of the solution containing the biochemically active substances. Moreover, the area of contact can be enlarged.
The above-mentioned mold is made of a composite material composed of biodegradable polymers, particles composed of the biodegradable material, porous particles or particles of a water-soluble material. The foregoing particles enhance penetration of the solution, enlarge the area of contact and provide a culture area for the microorganisms. Prior to or simultaneously with the biochemical degradation, the mold is irradiated with, for example, ultraviolet rays. Thus, the molecule chains of the biodegradable polymers are cut to collapse the polymers so as to enhance the biochemical degradation. Moreover, substances for enhancing the degradation are added to the biodegradable polymers.
The present invention is able to manufacture structures having a variety of shapes by using the characteristic of the mold made of the biodegradable material, that is, the characteristic with which the mold is degraded into liquid and gas.
If the mold made of the above-mentioned material is used as the core, the core can easily be degraded and removed. The hollow portions created by the core are required to have passages capable of removing the solution containing the biochemically active substances, liquid of the degraded substances and the gas. Therefore, a hollow structure having an arbitrary shape can easily be manufactured.
When the above-mentioned characteristics are used to surround, for example, a spherical core, with a prepreg made of the composite material so as to be filled into the mold, a strong hollow structure can be constituted. Since a hollow portion having an arbitrary shape can be formed, a structure having a multiplicity of hollow ribs or a structure in the form of an isogrid shape can easily be manufactured.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.